International Consolidated Airlines' (LON:IAG) British Airways unit cancelled and delayed flights at London's Heathrow yesterday, due to problems with a supplier's IT systems, Reuters has reported.
The second event, on Wednesday evening, was blamed on a problem with a British Airways computer system.
"We have apologised to our customers for the delay to their travel plans", British Airways said regarding the current cancellations and delays.
One traveller caught in the disruption said: "They just said to me "stay in the queue".
Hundreds of passengers were told to return to the airport on Thursday.
She added that flights are operating today, now the supplier "has resolved the issue", but didn't explain what the root cause was when IT Pro asked.
The control tower was evacuated and an airport spokesperson said: 'We are investigating what it means for flights landing and departing'.
Heathrow Airport said the alarm has been investigated, and "operations" have started to resume.
Terminal 5 was further affected by the situation - leading to an organisational nightmare for BA managers.
"We are doing all we can to keep any knock-on disruption to our services to a minimum and are sorry for the disruption to our customers' travel plans".
The disruption comes as airports across the country gear up for the busiest part of the year as the summer holiday season begins in earnest.
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